High intensity light sources, and particularly white high intensity light sources, are interesting for various applications including spots, stage-lighting, automotive lighting and digital light projection. For such purposes, it is possible to make use of so-called light concentrators where short wavelength light is converted to longer wavelengths in a highly transparent luminescent material. Such a transparent luminescent material is illuminated by LEDs to produce longer wavelengths within the luminescent material. Converted light, which will be waveguided in the luminescent material, is extracted from a surface leading to an intensity gain and thus brightness gain.
Document WO 2012/056382 A1 describes in one embodiment a lighting device for such a purpose and comprising a waveguide, one light source and a plurality of light outcoupling means. The waveguide may be provided with a luminescent material arranged on or in the waveguide and may thereby be configured to convert light from a light source into luminescent material emission.
The light output can then be increased by coupling in more light, by making the light guide longer and increase the number of LEDs that is used to illuminate the luminescent concentrator. However, as a result of self-absorption in the luminescent material as well as increased light outcoupling due to the LEDs, the larger, and particularly the longer, the light guide is, the more light will be lost, which in turn leads to a decrease in the intensity gain of the light emitted by the light guide and thus the light emitting device. Thus, the scalability of the light emitting device is radically decreased.